The virus that causes hepatitis B or serum hepatitis appears to infect only man. Hepatitis B virus ("HBV") infection in humans is widespread. In the United Kingdom, United States, and Western Europe, approximately 0.1% of all blood donors are chronic carriers of HBV. While the death rate due to viral hepatitis is not high (in 1975 in the United Kingdom it was 3 per million), there are indications that as many as 5% of the population in the United Kingdom and 15% of the population in the United States have been infected. In many African and Asian countries, up to twenty percent of the population are chronic carriers of HBV, and over fifty percent of all adults in those countries have been or are infected with HBV.
The hepatitis infection is transmitted by three general mechanisms: (1) by parenteral inoculation of infected blood or body fluids, either in large amounts as in blood transfusions or in minute amounts as through an accidental skinprick; (2) by close family or sexual contact; and (3) by some mothers, who infected during pregnancy, transmit the virus to their new-born children. Under natural conditions, HBV is not highly contagious. Transmission by inhalation occurs rarely, if ever.
Most HBV infections are subclinical. The clinical illness usually lasts three to six weeks and ranges in severity from mild to acute fulminating hepatitis followed by cirrhosis or death. Recovery from clinical and subclinical HBV infections is usually complete. However, serious long term consequences result in some cases: (1) approximately five percent of acute infections lead to chronic carriage of hepatitis B virus antigen with its continuing potential for infectivity to others and ongoing liver damage; and (2) it is likely that past infection with HBV may be wholly or partly responsible for the initiation of a significant proportion of HBV-seronegative cases of chronic active hepatitis, cirrhosis and primary liver carcinoma.
Recent advances in molecular biology have made it possible to introduce the DNA coding for specific non-bacterial eukaryotic proteins into bacterial cells. In general, with DNA other than that prepared via chemical synthesis, the construction of the recombinant DNA molecules comprises the steps of producing a single-stranded DNA copy (cDNA) or a purified messenger (mRNA) template for the desired protein; converting the cDNA to double-stranded DNA; linking the DNA to an appropriate site in an appropriate cloning vehicle and transforming an appropriate host with that recombinant DNA molecule. Such transformation permits the host to produce the desired protein. In addition, at least in the case of ovalbumin DNA, it is known that appropriate fusion of the particular DNA to a strong bacterial promoter or expression control sequence produces larger amounts of the desired ovalbumin protein, i.e., about 0.5 to 1% of the total protein mass of an E. coli cell (O. Mercereau-Puijalon et al., "Synthesis Of An Ovalbumin-Like Protein By Escherichia coli K12 Harboring A Recombinant Plasmid", Nature, 275, pp. 505-510 (1978) and T. H. Fraser and B. J. Bruce, "Chicken Ovalbumin Is Synthesized And Secreted By Escherichia coli", Proc. Natl. Acad. Sci. USA, 75, pp. 5936-5940 (1978)).
Several non-bacterial proteins and genes have been synthesized using recombinant DNA technology. These include a protein displaying rat proinsulin antigenic determinants (L. Villa-Komaroff et al., "A Bacterial Clone Synthesizing Proinsulin", Proc. Natl. Acad. Sci. USA, 75, pp. 3727-3731 (1978)), rat growth hormone (P. H. Seeburg et al., "Synthesis Of Growth Hormone By Bacteria", Nature, 276, pp. 795-798 (1978)), mouse dihydrofolate reductase (A. C. Y. Chang et al., "Phenotypic Expression in E. coli Of A DNA Sequence Coding For Mouse Dihydrofolate Reductase", Nature, 275, pp. 617-624 (1978)), somatostatin (K. Itakura et al., "Expression In Escherichia coli Of A Chemically Synthesized Gene For The Hormone Somatostatin", Science, 198, 1056-1063 (1977), United Kingdom Pat. specification Nos. 2,007,675A, 2,007,676A and 2,008,123A and cognate applications in other countries), and the A and B polypeptide chains of human insulin (D. V. Goeddel et al., "Expression In Escherichia coli Of Chemically Synthesized Genes For Human Insulin", Proc. Natl. Acad. Sci. USA, 76, pp. 106-110 (1979) and the United Kingdom and related patent specifications, supra).
None of the foregoing, however, is directed, as is this invention, toward the recombinant DNA synthesis of viral proteins such as hepatitis B virus antigens.
It is known that HBV infections cause development of antibodies to the antigens of the virus. These antibodies are the body's defense mechanism to the HBV infection. The development of such antibodies prior to exposure or rapidly in the case of potential exposure should substantially reduce and combat virus growth and spread in the patient.
A problem however in the artifically stimulated development of antibodies to the antigens of hepatitis B virus is the limited host range of the virus. For example, although highly infectious to man, experimental infection with hepatitis B virus has been achieved in only a few additional primates. And, the virus has not been propagated in tissue culture. This limited host range and inability to infect tissue culture cells has severely hampered both the characterization of the virus and the pathology of its infection and the development of rapid detection means and effective means of infection control and prevention.
While there have been some attempts to employ authentic HBV viral antigens, isolated from victims of the HBV infection, for the development of antibodies and detection of infection, these treatments are not generally available because of the limited supply of the active species. Furthermore, the use of human sources for these antigens is disfavored because of the well recognized contamination problems in using human isolates.